The invention of this application relates to bag valves, such as are used for filling bags with bulk particulate material. Such bags have a valve in a collapsible tubular form generally located in an end closure of the bag. More particularly, this invention relates to an induction heat sealable valve and to methods and apparatus for sealing of such valves.
Many particulate materials, such as powders or granules of cement, flour, seeds, grains, chemicals and the like are packaged and transported in sealed bags, for instance multi-walled paper bags. To facilitate filling, such bags have long been provided with valves, for instance in a collapsible tubular form in an end closure. In a convenient method for filling such bags with bulk particulate material, a nozzle is inserted through the valve to allow the particulate material to flow into the bag.
Although the valve may tend to collapse to some degree upon withdrawal of the nozzle, many efforts have been made to provide a more secure closure of the valve to preclude subsequent communication through the bag valve which may result, for instance, in the loss of material from the bag or the introduction of foreign material such as insects or other contaminants into the bag. Secure closures have been obtained, for instance, by providing extending sleeves on the valve which can be folded to seal the valve. Such folded sleeves often exhibit the undesirable characteristic of becoming unfolded, e.g. accidentally or otherwise, resulting in possible transfer of material through the valve.
Alternatively, such externally extending sleeves have been taped or glued generally at considerable expense of time and labor. In still other cases valves have been provided with wire springs to securely fold an internally extending sleeve as disclosed for instance in U.S. Pat. No. 4,111,354. Such wire spring seals do not assure that material cannot be transferred through the valve.
In still other cases, valves have been sealed by applying an adhesive to the interior peripheral surfaces of the valve, for instance after filling of the bag as disclosed in U.S. Pat. No. 4,394,207. Such adhesive application is not carried out without some risk of product contamination with the applied adhesive. Contamination is reduced by the use of releasable glue spots within a valve, for instance comprising a polyethylene line, as is disclosed in U.S. Pat. No. 4,049,191. Such releasable sealing, however, allows a sealed valve to be repeatedly broken and resealed.
The use of polymeric valve liners allows further opportunity for valve sealing, for instance by heating to fuse the polymeric liner. See for instance, U.S. Pat. Nos. 3,831,643, 4,003,188, and 4,066,108 which disclose the use of a pair of heated jaws for engaging a valve sleeve internally coated with a heat sensitive adhesive material. The crimped and heat sealed valve sleeve is then stuffed into a pocket on the side of the valve. See also U.S. Pat. No. 4,367,620 where a polymeric valve liner which is held in a collapse state by the application of vacuum through porous windows in the polymeric liner. Such methods are not without their disadvantages, for instance, slow heating and the possibility of thermal degradation of the bag.
Other methods of sealing have been applied to open top bags where opposing side walls are brought together and often sewn in the planar margin formed by the juxtaposed walls. Where such bags are laminates having a thermoplastic-coated, metal foil inner layer a fusion seal is possible. See U.S. Pat. No. 3,146,564 which discloses apparatus for pressing together the sewn top margins to allow commingling of the thermoplastic coating during induction heating. The opposing top margins are then passed through a series of opposing compression rolls to maintain contact of the inner surfaces and thus promote fusion of the opposing bag walls. Such methods and apparatus, which are used to join layers extending from the exterior of a bag, cannot be practiced on valves having layers lying within a wall of a bag. Accordingly, prior to this invention, there was no known way to practically apply induction heat sealing methods to filling valves which do not extend from a bag but rather lie within a bag wall.
It is an object of this invention to provide methods and apparatus for rapidly sealing by induction heating valves lying substantially within a wall of a bag.
Another object of this invention is to provide collapsible tubular laminates useful as sealable valves for protecting the integrity of materials stored in bags, such as multi-walled bags.
Still another object of this invention is to provide a bag with a valve that can be sealed rapidly without significantly adversely affecting the bag material, for instance by the application of excess heat.
A further object of this invention is to provide a seal in a bag valve that cannot be readily unfastened without destroying the valve or the bag, thereby providing a greater degree of assurance that there has been no loss of material from the bag or introduction of foreign material into the bag.
These and other objects of the invention will be more readily apparent from the following detailed description.